WebApplication.storeBufferedResponse does not check if sessionId is null. This could lead to wrong behaviors as it happens in the quickstart project. Let's say we have a stateless home page with page parameters that are populated inside page constructor. Under these conditions class WebPageRenderer will call storeBufferedResponse and will redirect the response to the final URL (line 289). But as the session is temporary, the buffered response is not consumed and WebPageRenderer will rise a warning (line 194).
I think we should check for null sessionId inside WebApplication or inside WebPageRender.